You've just met the security behind the SSH, or Secure (Socket) Shell protocol: matched-key RSA encryption. When you log into a server via SSH, the server identifies itself to your system and establishes matching encryption algorithms on both ends of the conduit-or the SSH tunnel, as the hipster system administrators call it. If either end of the tunnel gets messed up or updated, the next time you try connecting to the server it'll warn you that it's an unknown server, and if you're using Mac OS 10.3.x, it'll leave you hanging, which sounds like your situation; Mac OS 10.4 smartened up the SSH tunneling to accept a new identifier from a formerly known server.

BONUS TIP: A TLA (three-letter acronym) Explained

Since this month's lesson is pretty easy, we'll give you some bonus knowledge: RSA isn't an acronym; the protocol is named for its inventors, Ron Rivest, Adi Shamir, and Leonard Adleman.

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